Method and apparatus for sharpening forage harvester knives

ABSTRACT

A forage harvester has an axially horizontal cylinder-type cutterhead with a plurality of elongated angularly spaced and axially extending knives at the cutterhead periphery with parallel cutting edges generating a cylinder as the cutterhead rotates. A knife sharpening device is mounted on the harvester adjacent to the cutterhead and includes a sharpening stone adjustable into engagement with the knives at the cutterhead periphery and reciprocatable along the entire length of the knives parallel to the cutterhead axis. In operation the cutterhead is rotated so that the cutting edges are on the advance side of the knives. However, means are provided for reversing the rotation of the cutterhead while the knives are being sharpened so that the sharpening stone engages the heel portion of each knife before the cutting edge, the outward deflection of the sharpening stone due to the engagement with the knives providing a small degree of heel relief on the knives.

United States Patent Markham 51 July 18, 1972 [54] METHOD AND APPARATUSFOR SHARPENING FORAGE HARVESTER KNIVES [72] Inventor: David ReesMarkham, Ottumwa, Iowa [73] Assignee: Deere 8: Company, Moline, Ill.

[22] Filed: March 11, 1970 [211 App]. No.: 18,410

679,168 7/1901 Hoyt ..51/250 1,734,713 ll/l929 Carlson ..56/250X PrimaryExaminer-Willie G. Abercrombie Attorney-Vincent H. Harsha, Harold M.Knoth, William A. Murray and John M. Nolan [57] ABSTRACT A forageharvester has an axially horizontal cylinder-type cutterhead with aplurality of elongated angularly spaced and axially extending knives atthe cutterhead periphery with parallel cutting edges generating acylinder as the cutterhead rotates. A knife sharpening device is mountedon the harvester adjacent to the cutterhead and includes a sharpeningstone adjustable into engagement with the knives at the cutterheadperiphery and reciprocatable along the entire length of the knivesparallel to the cutterhead axis. In operation the cutterhead is rotatedso that the cutting edges are on the advance side of the knives.However, means are provided for reversing the rotation of the cutterheadwhile the knives are being sharpened so that the sharpening stoneengages the heel portion of each knife before the cutting edge, theoutward deflection of the sharpening stone due to the engagement withthe knives providing a small degree of heel relief on the knives.

13 Clains, 10 Drawing Figures PATENTED JUL] 8 I972 SHEET 1 [IF 2INVENTOR. DAVID R. MARKHAM FIG.3

PATENTEI] Jun 81972 SHEET 2 OF 2 FIG.4

FIG.6

FIG.5

INVENTOR. DAVID R. MARKHAM FIG.8

FIG.IO

FIG.?

METHOD AND APPARATUS FOR SI'IARPENING FORAGE HARVESTER KNIVES BACKGROUNDOF THE INVENTION This invention relates to forage harvesters and moreparticularly to an improved method and means for sharpening thecutterhead knives on a forage harvester.

Most currently manufactured forage harvesters utilize cylinder-typecutterheads, wherein a plurality of elongated an- 1 gularly spacedknives are mountedon the cutterhead with their cutting edges extendingin a generally axial direction at the cutterhead periphery. The crop isfed radially into the cutterhead over a stationary shear bar, whichregisters with the knife cutting edges. The knives are typicallyprovided with a heel relief, so that the heel or trailing edge of eachknife is offset inwardly from the cutting edge, whereby only the cuttingedge registers with the shear bar.

During operation of the machine, the knife cutting edges become dullquite rapidly, and, in order to maintain the efficiency of the machine,it is necessary that the knives be sharpened at relatively frequentintervals, sometimes as often as once a day. Thus, it has become commonto provide an integral knife sharpening apparatus on the machine capableof sharpening the knives without removing the knives from thecutterhead. Typically the sharpening apparatus comprises a sharpeningstone adjustable into engagement with the knives and reciprocatablealong the cutterhead periphery parallel to the cutterhead axis, thecutterhead being driven in its normal operating direction while thesharpening stone is reciprocated along the cutterhead periphery, therebyremoving material from the knives and restoring a sharp edge on theleading or cutting edge of each knife. Generally, the cutterhead isrotated at a reduced speed during the sharpening operation by reducingthe throttle setting of the engine which powers the forage harvester.However, this method of touching up the knives has created a problem, inthat the material removed is at the cutterhead periphery at and adjacentto the cutting edge, so that the heel relief on the knife is reduced.After repeated sharpenings, the heel relief disappears. In actualpractice, the problem is more acute, since as each knife engages thesharpening stone, the stone deflects outwardly as the knife passes bythe stone, so that more material is removed at the leading or cuttingedge of each knife than on the heel surface to the rear of the cuttingedge. Thus, a negative heel relief is produced on the sharpened surface,so that the cutting edge does not register with the shear bar, but theregistry occurs on the heel surface behind the cutting edge. The morenumerous the sharpenings, the greater the negative heel relief, so thatafter numerous sharpenings, there is a substantial negative heel relief,which greatly reduces the efiiciency of the harvester.

Thus, heretofore, it has been necessary to periodically remove theknives from the harvester to rebevel or regrind the knives and providethem with their proper heel relief. An alternate method overcoming thisproblem has been to provide relatively complicated and expensivesharpening devices which will sharpen the knives while still on thecutterhead and while the cutterhead is stationary, such devicesconventionally utilizing electric motors to drive a grinding wheel whichsharpens the knives at the proper angle.

SUMMARY OF THE INVENTION According to the present invention, an improvedmeans and method of sharpening the cutterhead knives are providedwherein the sharpened knives are provided with a heel relief withoutremoving the knives from the cutterhead. Specifically, the knives aresharpened by reversing the rotation of the cutterhead during thesharpening operation while using the typical adjustable andreciprocatable sharpening stone at the cutterhead periphery, so that thecutting edge of each knife is on the trailing edge of the knife duringthe sharpening operation.

An important feature of the invention resides in the provision of simpleand inexpensive means for driving the cutterhead in the reversedirection. More specifically, the engine, which normally drives thecutterhead, is also used to drive the cutterhead in a reverse direction,the drive reversal being accomplished by a relatively simple mechanismassociated with the normal drive train on the harvester.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. -1 is a somewhat schematic planview of a portion of a forage harvester embodying the invention, withportions of the cutterhead housing broken away to show a part of thecutterhead.

FIG. 2 is a side elevation section of the rear portion of the forageharvester as viewed along a line 2-2 of FIG. 1, but on a slightly largerscale.

FIG. 3 is a somewhat schematic plan view of a second embodiment of theinvention showing only the cutterhead housing portion of the forageharvester and the rear portion of a tractor operative to drive thecutterhead in a reverse direction, a portion of the cutterhead housingbeing broken away to show the schematically illustrated sharpeningmechanism.

FIG. 4 is a schematic plan view of a third embodiment of the inventionin a slightly different type of forage harvester.

FIG. 5 is a schematic section of a cutterhead knife before the knife isused.

FIG. 6 is a view similar to FIG. 5, but showing the knife after itsinitial use and after it has been somewhat dulled.

FIG. 7 is a view showing the knife in FIG. 6 after it has been sharpenedwith the prior art method of sharpening the knives on the cutterhead.

FIG. 8 is a view similar to FIG. 7, but showing the knife after repeatedsharpenings according to the prior art method.

FIG. 9 is a view similar to FIG. 7, but showing a knife having arelatively small amount of use, and after it has been sharpenedaccording to the present invention.

FIG. 10 is a side section of the knife sharpening apparatus during thesharpening operation according to the present invention, the knife beingsimilar to the knife shown in FIG. 9, but after numerous sharpenings.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is embodied in aforage harvester having a mobile main frame 10 mounted on right and leftsupport wheels 12 and 14 respectively. The harvester is a pull type, PTOoperated machine, and accordingly, the main frame includes afore-and-aft extending draft portion, only the rearward part of which isshown in the drawings and indicated by the numeral 16. As isconventional, the draft portion includes a fore-and-aft extending draftmember or tongue connectable to the drawbar of the towing tractor. Theoverall construction of the forage harvester is substantially similar tothat illustrated in US. Pat. No. 3,377,785, which is also assigned tothe assignee herein. As is also conventional, a fore-and-aft drive shaft18 extends over the draft member and is connectable at its forward endto the tractor power take-off mechanism via a power shaft which includesa pair of universal joints.

Mounted on the right side of the main frame 10 is a cutterhead housing,indicated in its entirety by the numeral 20. An axially transversecylinder-type cutterhead 22 is mounted within the housing 20 andincludes an axial shaft 24 journaled in and extending through the sidewalls of the housing and a plurality of elongated, generally axiallyextending knives 26 mounted on a pair of knife supports 28 carried bythe shaft 24. The knives generate a cylinder as the cutterhead rotatesand, as best seen in FIG. 1, are of the helical type, the constructionof the cutterhead being well known and therefore being onlyschematically illustrated.

The cutterhead housing 20 includes a top wall 30 having a raisable door32 adjacent its rearward end. A removable panel 33 is mounted within thehousing immediately above and adjacent to the cutterhead periphery andis removable through the door 32 in a well known manner. The lowerhousing portion or band 34 is disposed immediately below the cutterheadin close proximity to the cutterhead periphery and includes an aperturedscreen 36 extending across the housing outlet 37. A

shear bar 38 spans the width of the cutterhead at the forward end of thelower band 34, the gap between the shear bar and the front end of theremovable panel 33 forming an inlet to the cutterhead. As is well known,the shear bar is adjustable and is maintained in registry with thecutterhead knives.

A harvesting header 42, which is schematically illustrated herein, ismounted at the forward end of the cutterhead housing and operates toremove the crop from the field in a well known manner, the particulartype of header utilized depending on the crop being harvested. Theheader moves the crop to feed roll means (not shown), which feed thecrop rearwardly through the inlet 40 and over the shear bar 38. As thecrop moves past the shear bar, it is reduced by the cutterhead and isimpelled through the screen 38 into an auger-type conveyor 44, whichmoves the crop laterally across the forage harvester and feeds it to ablower-type elevator 46, which impells the crop material upwardly andrearwardly into a collecting vehicle.

The power for the above driven components is supplied through thetractor PTO through a drive train, the drive shaft 18, which isconnected to the tractor PTO, serving as the input to the drive train.The drive shaft 18 drives a transverse drive shaft 48 through aconventional gear box 50 at the rear end of the drive shaft 18. Thedrive shaft 48, in turn, is connected to the cutterhead shaft 24 througha transmission 52 and an overrunning one-way clutch 54. The transmission52 connects the shaft 48 to driving components for the feed rolls andthe header 42.

The blower 46 is driven by a transverse shaft 56, which, in turn, isconnected to and driven by the cutterhead shaft 24 by means of a chaindrive 57 at the right-hand end of the machine. As is apparent, the shaft56 is parallel to and rearwardly of the drive shaft 48, and the chaindrive includes sprockets mounted on the ends of both shafts andconnected by a conventional chain, so that the drive shaft 56 is drivenin the same direction as the shaft, 48 and the cutterhead shaft 24. Aseparable coupling58 is provided in the drive shaft 48 between thetransmission 52 and the gear box 50, and a spur gear 60 is mounted onthe shaft 48 between the coupling 58 and the gear box 50 and isselectively connectable thereto. A second spur gear 62 is attached tothe shaft 56 and meshes with the gear 60, and a second separablecoupling 64 is provided in the shaft 56 between the gear 62 and theblower 46.

The tractor power off rotates in a clockwise direction, when viewed by aperson standing at the rear of the tractor and looking forwardly, sothat the drive shaft 18 also rotates in a clockwise direction whenviewed from the rear of the forage harvester and looking forwardly(upwardly in FIG. 1). Thus, when the coupling 58 is connected, as shownin FIG. 1, the shaft 48 and the cutterhead shaft 24 connected theretoare driven in a clockwise direction, as viewed from the right hand endof the machine and also as shown in FIG. 2. This, of course, is thenormal or forward operating direction of rotation for the cutterhead.When the coupling 58 is connected as shown, the gear 60 is alwaysdisconnected from the shaft 48. Preferably, the same removable elementor pin is used to alternately couple the gear 60 to the shaft 48 or toconnect the coupling 58, so that it is impossible to simultaneouslyconnect the coupling 58 and the gear to the shaft 48. When the gear 60is connected to the shaft 48 as indicated by the dotted line position ofthe pin in FIG. 1, the right end of the shaft 48 is disconnected fromthe left end, which drives the blower drive shaft '56 through themeshing gears 60 and 62 in a counterclockwise direction as viewed fromthe right-hand end of the machine. When the shaft 56 is thus reversed,the coupling 64 is preferably disconnected so that the blower 46 is. notoperated. The reverse or counter-clockwise rotation of the shaft 56 istransmitted to the cutterhead shaft 24 through the chain drive 57, sothat the cutterhead is rotated in a reverse direction (counter-clockwisewhen viewed from the right end of the machine and in FIG. 2.). Theover-running one-way clutch .54 prevents the reverse rotation of thecutterhead shaft from being transmitted to the disconnected end of theshaft 48 and the transmission 52. Thus, by simply disconnecting thecouplings 58 and 64 and connecting the gear 60 to the shaft 48, therotation of the cutterhead shaft can be reversed.

An alternate method of reversing the rotation of the cutterhead shaft isshown in FIG. 3, wherein the forage harvester' is the same as shown inFIG. 1 except that the separable coupling 58 and the gears 60 and 62 areomitted. Thus, in normal operation when the tractor is connected to thedrive shaft 18, the shaft 48 and the cutterhead shaft 24 connectedthereto are driven in the normal forward direction. However, a splineconnection 65 is provided at the right end of the blower drive shaft 56,so that the shaft can be connected to and driven by the power take-off66 of a tractor, only the rearward portion of which is shown in FIG. 3and identified by the numeral 67, the tractor power take-off mechanism66 being connected to the spline connection 65 through a conventionaluniversal joint-type power shaft 68, which can also be used to connectthe front end of the shaft 18 to the power take-off mechanism.

A third embodiment of the invention is shown in FIG. 4, which is aschematic illustration of a forage harvester which is essentially thesame as the harvester shown in FIGS. 1 and 3 except that it illustratesa cut and throw" type machine, wherein the cutterhead 22 also serves toimpel the reduced material upwardly and rearwardly through a dischargespout 69, eliminating the cross auger 44 and the blower 46. Thecutterhead is again driven in a forward direction by means of a driveshaft 18 connected to the tractor power take-off mechanism, the shaft 18being connected to the cutterhead shaft 24 through the drive shaft 48,the transmission 52, and the over-running clutch'54. The separablecoupling 58 is again connected, as illustrated during normal operationof the machine. For a reverse drive for the cutterhead, a mum tershaft70 is provided on the machine parallel to the shaft 48. The countershaft70 is normally not driven, but when the coupling 58 is disconnected, theshaft 70 is driven in the same direction as the left end of the shaft 48through a conventional chain drive 72, the input sprocket of which canbe selectively coupled to the left-hand or driven portion of the shaft48 when the coupling 58 is disconnected. The countershaft 70 has a spurgear 74 at its right-hand end, meshing with a spur gear 76, which can beselectively coupled to the cutterhead shaft 24 to drive the cutterheadin the opposite direction from the shaft 70. Thus, to obtain reverserotation of the cutterhead, the coupling 58 is disconnected, while thechain drive 72 is connected to the shaft 48 and the gear 76 is connectedto the shaft Of course, other mechanisms for reversing the cutterheaddrive could be provided within the scope of the invention, the threeillustrated drives providing relatively inexpensive and simple means forreversing the drives.

The detailed construction of the outer portions of the knives is shownin FIGS. 5-10 inclusive, which illustrates the knives as viewed from theright end of the cutterhead, the normal or forward direction of rotationof the knives being in a clockwise direction. Each knife has a cuttingedge 80 at the outer periphery of the cutterheadand on the leading edgeof the knife during normal rotation of the cutterhead. Each knife alsohas a heel edge 82, trailing the cutting edge 80 adjacent to the outerperiphery of the cutterhead and a heel surface 84. extending between theheel edge 82 and the cutting edge 80.

FIG. 5 illustrates the preferred and original configuration of eachknife, wherein the heel surface 84 is inclined inwardly away from theperiphery of the cutterhead, so that the heel edge 82 is locatedradially inwardly from the cutting edge 80. When the machine is new, theheel relief or bevel, which is denoted by the angle A in FIG. 5, ispreferably approximately 15. It is well known to provide such a reliefon cutting knives, so that only the cutting edge 80 registers with theshear bar 38, thereby increasing the efficiency of the cutterhead.During actual use, the cutting edge 80 is rapidly blunted, as shown inFIG. 6, which represents a cutterhead knife after a relatively shortperiod of use. Obviously, the blunted cutting edge 80 reduces theefficiency of the harvester, and therefore, a sharpening mechanism,illustrated generally by the numeral 86, is conventionally provided onthe machine for touching up the cutting edge 80 at relatively frequentintervals.

The construction of such sharpening mechanisms 86 is well known, twotypical sharpening mechanisms being shown in US. Pat. Nos. 3,331,167 and3,370,688. The construction of the sharpening mechanism is somewhatschematically illustrated in FIG. 3 and is shown in much greater detailin FIG. 10. The sharpening mechanism includes an abrasive sharpeningstone 88 mounted in a carriage 90 which is slidably mounted on a pair ofparallel rods 92 and 94 which span the cutterhead housing parallel toand immediately above the cutterhead 22. The rod 92 is fixed, but therod 94 is supported at its opposite ends on a pair of levers 96swingable about the axis of the rod 92, whereby the entire assembly isvertically adjustable in an are about the axis of the rod 92. Thevertical adjustment of the assembly is accomplished by rotation of athreaded crank 98, which extends through a threaded opening in thecutterhead housing top wall 30 and is connected to one of the levers 96,whereby rotation of the crank 98 raises or lowers the sharpeningmechanism about the axis of the rod 92.

During the operation of the machine, the sharpening mechanism is swungupwardly out of the way of the cutterhead and the removable panel 33 isdisposed between the sharpening mechanism and the cutterhead. When theoperator decides to sharpen the knives, the panel 33 is removed throughthe door 32, and the sharpening mechanism is adjusted downwardly untilthe stone engages the rotating knives. The stone is then reciprocatedback and forth across the width of the cutterhead by means of a rod 100,which is attached to the carriage 90 and extends laterally through theside of the cutterhead housing. During normal operation, the cutterheadon the machine such as illustrated in FIGS. 1, 2 and 3, is rotated atapproximately 850 rpm, while the preferred grinding speed isapproximately 600 rpm. Thus, it is necessary to throttle down thetractor to some extent to obtain the preferred grinding speed during thesharpening operation.

Heretofore, the cutterhead has been rotated in a forward or normaloperating direction during the sharpening operation, so that the cuttingedge 80 was also on the leading edge of the knife during the sharpeningoperation. However, when the knives are sharpened in this manner, thesharpened portion of the knife could be expected to have the same radiusas the cutterhead, thus reducing some of the heel relief on the knife.In actual practice, it has been found that the sharpened knives havesomewhat the configuration of the knife shown in FIG. 7, wherein morematerial is removed from the leading part of the knife, since, when thecutting edge 80 engages the sharpening stone 88, the force of engagementdeflects the sharpening mechanism 86 outwardly due to play in themechanism or deflects the knife inwardly. Thus, not only is the heelrelief lost, but a negative heel relief develops, which has been foundto be approximately 3 as indicated by the angle B in FIG. 7. After onlya few sharpenings, the knives have the configuration shown in FIG. 7.However, after numerous sharpenings, the entire heel relief is gone asshown in FIG. 8 and there is a substantial negative heel relief or bevelB, whereby only the heel 82 of the knife can be brought into registrywith the shear bar, the cutting edge 80 being spaced inwardly from theshear bar. This, of course, drastically reduces the efficiency of thecutterhead and increases the power consumed by the machine. The problemheretofore has been alleviated only by removing the knives from themachine and restoring the bevel, or by utilizing a relatively complexand expensive sharpening mechanism to sharpen the knives while on themachine.

When the knives are sharpened according to the present invention,wherein the direction of rotation of the cutterhead is reversed duringthe sharpening operation, the inherent negative heel relief or bevel isreversed to again provide a positive heel relief or bevel. Thus, if,after initial wear, the knives were sharpened when the cutterhead wasdriven in reverse, the stone 88 would initially engage the knifesomewhere along the heel surface 84, and the subsequent deflection ofthe stone would provide a positive heel relief, which has been found tobe approximately 3 as again illustrated by the angle B in FIG. 9. Theportion of knife not engaged by the sharpening mechanism would retainits approximately 15 heel relief as indicated by the angle A. Afternumerous sharpenings, the original heel relief would entirely disappear,and the 3 heel relief would extend across the entire heel surface 84, asshown in FIG. 10. Although the larger heel relief indicated by the angleA is desirable, it has been found that the lesser heel relief, indicatedby the angle B, as provided by sharpening the knives in the abovemanner, is satisfactory. Thus, the present method of sharpening knives,and the reversing mechanism for utilizing said method, provide a simpleand inexpensive method for maintaining the proper cutting edge on theforage harvester knives.

I claim:

1. In a forage harvester having a cutterhead housing and an axiallyhorizontal cylinder-type cutterhead joumaled in the housing and having aplurality of elongated, angularly spaced knives with parallel cuttingedges at the cutterhead periphery, each knife having a heel surface atthe cutterhead periphery immediately adjacent to and trailing thecutting edge when the cutterhead is rotated in a forward operatingdirection, the improvement comprising: a knife sharpening element havinga width extending in a circumferential direction relative to thecutterhead that is less than five times the circumferential width ofsaid heel surfaces; means mounting the element for adjustment into firmengagement with the knives when the cutterhead is rotating and foroutward resilient yielding, and inward rebounding; and reversible drivemeans for selectively driving the cutterhead in a forward operatingdirection or a reverse direction, the sharpening element engaging eachknife inwardly of the cutting edge when the cutterhead is driven inreverse so that the intermittent force of engagement with the successiveknives causes the sharpening element to yield outwardly as each heelsurface moves along the sharpening element so as to grind a heel reliefextending from each cutting edge, the sharpening element reboundinginwardly after each knife clears the element.

2. The invention defined in claim I wherein the cutterhead includes anaxial cutterhead shaft and the drive means includes a first drive shaftdriven by the power source in one direction, means for selectivelyconnecting the first drive shaft to the cutterhead shaft to drive thecutterhead in its forward direction; a second drive shaft parallel tothe first drive shaft; and means for selectively connecting the seconddrive shaft to the first drive shaft and the cutterhead shaft to drivethe cutterhead in said reverse direction.

3. The invention defined in claim 2 wherein the means con necting thesecond drive shaft to the first drive shaft comprises a drive mechanismoperative to drive the second drive shaft in the opposite direction fromthe first drive shaft and the means for connecting the second driveshaft to the cutterhead shaft comprise a drive mechanism operative todrive the cutterhead shaft in the same direction as the second driveshaft.

4. The invention defined in claim 2 wherein the forage harvesterincludes blower means for discharging crop material reduced by thecutterhead and the second drive shaft is drivingly connected to theblower means.

5. The invention defined in claim 2 wherein the means connecting thesecond drive shaft to the first drive shaft includes an endless flexibleelement operative to drive the second drive shaft in the same directionas the first drive shaft and the means connecting the second drive shaftto the cutterhead shaft includes gear means operative to drive thecutterhead in the opposite direction from the second drive shaft.

6. The invention defined in claim 5 wherein the drive means includes atractor having a power take-off mechanism, a drive train connected tothe cutterhead and including first and second alternate power inputmeans, and means for alternate- 1y connecting the power take-ofimechanism to the first or the second power input means to respectivelydrive the cutterhead in the forward and reverse directions.

7. The method of sharpening the knives of a forage harvester cutterheadwherein the cutterhead is of generally cylindrical structure rotatablein a normal forward direction and having a plurality of uniformlyangularly'spaced elongated, parallel knives provided respectively withinitially sharp cutting edges lying on the cutterhead periphery andoperative as leading edges cooperative with a fixed shear bar duringnormal forward operation, each knife having a heel surface trailing itscutting edge and receding radially and circumferentially inwardly of thecutterhead periphery to a terminal trailing edge, and a knife sharpeningelement adjustable into engagement with the knives, said methodcomprising: continuously rotating the cutterhead in a reverse directionat a relatively high speed, and adjusting the sharpening element intofirm engagement with the knives while the cutterhead is so rotatingreversely so that portions of the respective knives behind therespective dulled cutting edges individually and successively engage thesharpening element respectively prior to elementengagement by therespective dulled edges so as to cause the sharpening element tosuccessively deflect outwardly and rebound inwardly at intervalsaccording to cutterhead speed and angular spacing of the knives so as toprovide heel relief extending from the new cutting edges.

8. The invention defined in claim 7 where the cutterhead is driven at aslower rotational speed in said reverse direction than in said normaloperating direction.

9. In a pull-type forageharvester adapted to be towed and powered by atractor having a uni-directional power take-off mechanism, saidharvester including a generally fore-and-aft drive shaft connectible tothe power take-off mechanism, an axially horizontal transverselyoriented cutterhead including an axial shaft and a plurality of parallelelongated knives with cutting edges at the cutterhead peripherygenerating a cylinder as the cutterhead rotates, and a knife sharpeningmeans including a sharpening element adjustable into engagement with theknives as the cutterhead rotates to remove material from the knives, theimprovement comprising: a first transverse drive shaft operativelyconnected to and driven by the fore-and-aft drive shaft; a firstdisengageable connecting means for selectively drivingly connecting thefirst transverse drive shaft to the cutterhead shaft to drive thecutterhead in a normal operating direction with the knife cutting edgesat the leading edges of the knives; a second transverse drive shaftgenerally parallel to the first drive shaft; a second disengageableconnecting means for selectively drivingly connecting the second driveshaft to the first drive shaft to drive the second drive shaft in theopposite direction from the first; and means operatively connecting thesecond drive shaft to the cutterhead so that the cutterhead is driven inthe same direction as the second drive shaft so that the cutterhead isdriven in a reverse direction when the first connecting means isdisengaged to disconnect the first drive shaft from the cutterhead shaftand the second connecting means is engaged to reversely drive the seconddrive shaft, the sharpening element being engageable with the reverselydriven cutterhead to facilitate the sharpening of the knives.

10. The invention defined in claim 9 wherein the means connecting thesecond drive shaft to the first drive shaft includes an endless flexibleelement.

1 l. The invention defined in claim 9 wherein the forage harvesterincludes blower means for discharging crop material reduced by thecutterhead and the second drive shaft is drivingly connected to theblower means.

12. In a forage harvester having a cutterhead housing and an axiallyhorizontal cylinder-type cutterhead journaled in the housing and havinga plurality of elongated, angularly spaced knives with parallel cuttingedges at the cutterhead periphery generating a cylinder as thecutterhead rotates, each knife having an outer portion inclinedoutwardly and in a forward operating direction and including a heelsurface immediately ad acent to and trailing the cutting edge and havinga substantially greater width than the thickness of the outer portion,the improvement comprising: a knife sharpening element having a lengthless than one-half the axial length of the cutterhead and acircumferential width extending less than 20 relative to the cutterheadaxis; means mounting the sharpening element on the harvester forreciprocation lengthwise of the cutterhead, for adjustment into firmengagement with the knives while the cutterhead is rotating and forresilient outward yielding relative to the knives; and reversible drivemeans operatively associated with the cutterhead for selectively drivingthe cutterhead in a forward operating direction or in a reversedirection at a speed above 60 rpm, so that the sharpening elementengages the outer portion of each knife before the cutting edge 7 whenthe element is adjusted into a position wherein it extends inwardly ofthe cutting edges and the cutterhead is driven in the reverse direction,the force of engagement between each knife and the sharpening elementcausing the element to yield outwardly as the knife moves along theelement and rebounds inwardly when the cutting edge clears the elementso that a heel relief is provided extending from each sharpened cuttingedge.

13. [n a forage harvester having a power source, a cutterhead housingand an axially horizontal cylinder-type cutterhead journaled in thehousing and having a cutterhead shaft and a plurality of elongated,angularly spaced knives with parallel cutting edges at the cutterheadperiphery generating a cylinder as the cutterhead rotates, each knifehaving a heel surface immediately adjacent to and trailing the cuttingedge when the cutterhead is rotated in a forward operating direction,the improvement comprising: a sharpening element having a lengthsubstantially less than the axial length of the cutterhead and acircumferential width extending less than 20 relative to the cutterheadaxis; means mounting the sharpen ing element on the harvester forreciprocation for the axial length of the cutterhead, for adjustmentinto firm engagement with the knives, and for resilient outward yieldingof the sharpening element; and a reversible drive train, operativelyconnecting the power source to the cutterhead shaft and including afirst drive shaft driven by the power source in one direction, a seconddrive shaft parallel to the first drive shaft, means operativelyconnecting the second drive shaft to the cutterhead shaft, meansexclusive of the second drive shaft for selectively connecting the firstdrive shaft to the cutterhead shaft to drive the cutterhead in itsforward direction, and means for selectively connecting the second driveshaft to the first drive shaft to drive the cutterhead in said reversedirection, the sharpening element engaging successive knives inwardly ofthe cutting edges when it is adjusted into firm engagement with theknives and the cutterhead is rotated in reverse so that the force ofengagement causes the element to resiliently yield outwardly as eachknife moves along the sharpening element and rebounds inwardly when theknife clears the sharpening element to generate heel relief extendingfrom each cutting edge.

1. In a forage harvester having a cutterhead housIng and an axiallyhorizontal cylinder-type cutterhead journaled in the housing and havinga plurality of elongated, angularly spaced knives with parallel cuttingedges at the cutterhead periphery, each knife having a heel surface atthe cutterhead periphery immediately adjacent to and trailing thecutting edge when the cutterhead is rotated in a forward operatingdirection, the improvement comprising: a knife sharpening element havinga width extending in a circumferential direction relative to thecutterhead that is less than five times the circumferential width ofsaid heel surfaces; means mounting the element for adjustment into firmengagement with the knives when the cutterhead is rotating and foroutward resilient yielding, and inward rebounding; and reversible drivemeans for selectively driving the cutterhead in a forward operatingdirection or a reverse direction, the sharpening element engaging eachknife inwardly of the cutting edge when the cutterhead is driven inreverse so that the intermittent force of engagement with the successiveknives causes the sharpening element to yield outwardly as each heelsurface moves along the sharpening element so as to grind a heel reliefextending from each cutting edge, the sharpening element reboundinginwardly after each knife clears the element.
 2. The invention definedin claim 1 wherein the cutterhead includes an axial cutterhead shaft andthe drive means includes a first drive shaft driven by the power sourcein one direction, means for selectively connecting the first drive shaftto the cutterhead shaft to drive the cutterhead in its forwarddirection; a second drive shaft parallel to the first drive shaft; andmeans for selectively connecting the second drive shaft to the firstdrive shaft and the cutterhead shaft to drive the cutterhead in saidreverse direction.
 3. The invention defined in claim 2 wherein the meansconnecting the second drive shaft to the first drive shaft comprises adrive mechanism operative to drive the second drive shaft in theopposite direction from the first drive shaft and the means forconnecting the second drive shaft to the cutterhead shaft comprise adrive mechanism operative to drive the cutterhead shaft in the samedirection as the second drive shaft.
 4. The invention defined in claim 2wherein the forage harvester includes blower means for discharging cropmaterial reduced by the cutterhead and the second drive shaft isdrivingly connected to the blower means.
 5. The invention defined inclaim 2 wherein the means connecting the second drive shaft to the firstdrive shaft includes an endless flexible element operative to drive thesecond drive shaft in the same direction as the first drive shaft andthe means connecting the second drive shaft to the cutterhead shaftincludes gear means operative to drive the cutterhead in the oppositedirection from the second drive shaft.
 6. The invention defined in claim5 wherein the drive means includes a tractor having a power take-offmechanism, a drive train connected to the cutterhead and including firstand second alternate power input means, and means for alternatelyconnecting the power take-off mechanism to the first or the second powerinput means to respectively drive the cutterhead in the forward andreverse directions.
 7. The method of sharpening the knives of a forageharvester cutterhead wherein the cutterhead is of generally cylindricalstructure rotatable in a normal forward direction and having a pluralityof uniformly angularly spaced elongated, parallel knives providedrespectively with initially sharp cutting edges lying on the cutterheadperiphery and operative as leading edges cooperative with a fixed shearbar during normal forward operation, each knife having a heel surfacetrailing its cutting edge and receding radially and circumferentiallyinwardly of the cutterhead periphery to a terminal trailing edge, and aknife sharpening element adjustable into engagement with the knives,said method comprising: continuoUsly rotating the cutterhead in areverse direction at a relatively high speed, and adjusting thesharpening element into firm engagement with the knives while thecutterhead is so rotating reversely so that portions of the respectiveknives behind the respective dulled cutting edges individually andsuccessively engage the sharpening element respectively prior toelement-engagement by the respective dulled edges so as to cause thesharpening element to successively deflect outwardly and reboundinwardly at intervals according to cutterhead speed and angular spacingof the knives so as to provide heel relief extending from the newcutting edges.
 8. The invention defined in claim 7 where the cutterheadis driven at a slower rotational speed in said reverse direction than insaid normal operating direction.
 9. In a pull-type forage harvesteradapted to be towed and powered by a tractor having a uni-directionalpower take-off mechanism, said harvester including a generallyfore-and-aft drive shaft connectible to the power take-off mechanism, anaxially horizontal transversely oriented cutterhead including an axialshaft and a plurality of parallel elongated knives with cutting edges atthe cutterhead periphery generating a cylinder as the cutterheadrotates, and a knife sharpening means including a sharpening elementadjustable into engagement with the knives as the cutterhead rotates toremove material from the knives, the improvement comprising: a firsttransverse drive shaft operatively connected to and driven by thefore-and-aft drive shaft; a first disengageable connecting means forselectively drivingly connecting the first transverse drive shaft to thecutterhead shaft to drive the cutterhead in a normal operating directionwith the knife cutting edges at the leading edges of the knives; asecond transverse drive shaft generally parallel to the first driveshaft; a second disengageable connecting means for selectively drivinglyconnecting the second drive shaft to the first drive shaft to drive thesecond drive shaft in the opposite direction from the first; and meansoperatively connecting the second drive shaft to the cutterhead so thatthe cutterhead is driven in the same direction as the second drive shaftso that the cutterhead is driven in a reverse direction when the firstconnecting means is disengaged to disconnect the first drive shaft fromthe cutterhead shaft and the second connecting means is engaged toreversely drive the second drive shaft, the sharpening element beingengageable with the reversely driven cutterhead to facilitate thesharpening of the knives.
 10. The invention defined in claim 9 whereinthe means connecting the second drive shaft to the first drive shaftincludes an endless flexible element.
 11. The invention defined in claim9 wherein the forage harvester includes blower means for dischargingcrop material reduced by the cutterhead and the second drive shaft isdrivingly connected to the blower means.
 12. In a forage harvesterhaving a cutterhead housing and an axially horizontal cylinder-typecutterhead journaled in the housing and having a plurality of elongated,angularly spaced knives with parallel cutting edges at the cutterheadperiphery generating a cylinder as the cutterhead rotates, each knifehaving an outer portion inclined outwardly and in a forward operatingdirection and including a heel surface immediately adjacent to andtrailing the cutting edge and having a substantially greater width thanthe thickness of the outer portion, the improvement comprising: a knifesharpening element having a length less than one-half the axial lengthof the cutterhead and a circumferential width extending less than 20*relative to the cutterhead axis; means mounting the sharpening elementon the harvester for reciprocation lengthwise of the cutterhead, foradjustment into firm engagement with the knives while the cutterhead isrotating and for resilient outward yielding relative to the knives; andreversible drive means operativeLy associated with the cutterhead forselectively driving the cutterhead in a forward operating direction orin a reverse direction at a speed above 60 rpm, so that the sharpeningelement engages the outer portion of each knife before the cutting edgewhen the element is adjusted into a position wherein it extends inwardlyof the cutting edges and the cutterhead is driven in the reversedirection, the force of engagement between each knife and the sharpeningelement causing the element to yield outwardly as the knife moves alongthe element and rebounds inwardly when the cutting edge clears theelement so that a heel relief is provided extending from each sharpenedcutting edge.
 13. In a forage harvester having a power source, acutterhead housing and an axially horizontal cylinder-type cutterheadjournaled in the housing and having a cutterhead shaft and a pluralityof elongated, angularly spaced knives with parallel cutting edges at thecutterhead periphery generating a cylinder as the cutterhead rotates,each knife having a heel surface immediately adjacent to and trailingthe cutting edge when the cutterhead is rotated in a forward operatingdirection, the improvement comprising: a sharpening element having alength substantially less than the axial length of the cutterhead and acircumferential width extending less than 20* relative to the cutterheadaxis; means mounting the sharpening element on the harvester forreciprocation for the axial length of the cutterhead, for adjustmentinto firm engagement with the knives, and for resilient outward yieldingof the sharpening element; and a reversible drive train operativelyconnecting the power source to the cutterhead shaft and including afirst drive shaft driven by the power source in one direction, a seconddrive shaft parallel to the first drive shaft, means operativelyconnecting the second drive shaft to the cutterhead shaft, meansexclusive of the second drive shaft for selectively connecting the firstdrive shaft to the cutterhead shaft to drive the cutterhead in itsforward direction, and means for selectively connecting the second driveshaft to the first drive shaft to drive the cutterhead in said reversedirection, the sharpening element engaging successive knives inwardly ofthe cutting edges when it is adjusted into firm engagement with theknives and the cutterhead is rotated in reverse so that the force ofengagement causes the element to resiliently yield outwardly as eachknife moves along the sharpening element and rebounds inwardly when theknife clears the sharpening element to generate heel relief extendingfrom each cutting edge.